Shark Ecology 109
■ Lateral line—A copepod lives inside the lateral line canals of the Por-
beagle.
■ Spiracles—Three families of copepods and some leeches live inside
these small breathing holes on the top of the head of some elasmo-
branchs.
■ Gills and gill chambers—Gills are infested with leeches, roundworms,
ostracods, Argulus fish lice, isopods, digenean flukes, monogenean flat-
worms, an occasional tapeworm, and a host of copepods from 11 dif-
ferent families. In Blue Sharks, some copepod species live only on the
walls between the gills, others on small gill filaments, and others in
the channels of outflowing water; still others draw blood from specific
blood vessels in the gills.
■ Digestive system—The different regions of the digestive system, from
mouth to rectum, each have their own catalogue of specific parasites.
The mouth and esophagus are home to leeches (some of which occur
in only one shark or ray species), copepods, flukes, flatworms, round-
worms, and barnacles. The stomach, despite its hostile chemical nature,
houses flatworms, roundworms, spiny-headed worms, isopods, and
numerous tapeworms. The spiral valve intestine has its own group of
parasites, including spiny-headed worms, flukes, flatworms, 50 species
of roundworms, and several hundred tapeworm species, some of which
live only in specific regions of the spiral valves. One family of tapeworms
lives only in chimaeras. One genus of spiny-headed worms is specific
to the potamotrygonid freshwater stingrays of South America. Some
batoid skates and rays can house as many as 10 species of tapeworms
in the spiral valve. The rectum and cloaca at the posterior end have
their own list of flukes and flatworms, copepods, leeches, and isopods.
■ Gall bladder, bile ducts, pancreatic ducts, liver, etc.—A few flukes, tape-
worms, and nematodes occur only in these organs and tissues. One
nematode also lives in the spleen of the Big Skate (Raja microocellata),
and roundworms have been found in shark kidneys. The body muscles
of sharks are relatively parasite free, except for an occasional round-
worm, unlike the situation in bony fishes.
■ Heart and blood vessels—The circulatory system is occupied by round-
worms, flukes, flatworms, mites, isopods, and an occasional eel (see be-
low).
■ Reproductive tracts—Male gonads are relatively parasite free (an oc-
casional tapeworm has been found); females house nematodes, tape-
worms, flatworms, flukes, leeches, copepods, and isopods variously in
their ovaries, oviducts, and uterus. Developing embryos are already
parasitized externally by leeches and copepods.